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Chlorophyll Fluorescence as a Possible Tool for Salinity Tolerance Screening in Barley (Hordeum vulgare L.)

The application of chlorophyll fluorescence measurements to screening barley (Hordeum vulgare L.) genotypes for salinity tolerance has been investigated. Excised barley leaves were cut under water and incubated with the cut end immersed in water or in a 100-mM NaCl solution, either in the dark or in high light. Changes in rapid fluorescence kinetics occurred in excised barley leaves exposed to the saline solution only when the incubation was carried out in the presence of high light. Fluorescence changes consisted of decreases in the variable to maximum fluorescence ratio and in increases in the relative proportion of variable fluorescence leading to point I in the Kautsky fluorescence induction curve. These relative increases in fluorescence at point I appeared to arise from a delayed plastoquinone reoxidation in the dark, since they disappeared after short, far-red illumination, which is known to excite photosystem I preferentially. We show that a significant correlation existed between some fluorescence parameters, measured after a combined salt and high-light treatment, and other independent measurements of salinity tolerance. These results suggest that chlorophyll fluorescence, and especially the relative fluorescence at point I in the Kautsky fluorescence induction curve, could be used for the screening of barley genotypes for salinity tolerance.

Organic acids and Fe deficiency : a review

Organic acid concentrations often increase with iron deficiency in different plant parts such as roots, leaves and stem exudates. The review summarises data available on the changes in the concentrations of organic anions in plants with iron deficiency and the effects of these changes in plant metabolism. The paper reviews data available in the literature on the changes in xylem and apoplasmic fluid composition with iron deficiency, both in plants grown in controlled conditions and in the field, and discusses the possible ways of iron complexation and transport in these compartments. The characteristics of the iron reduction and uptake by the iron-deficient leaf mesophyll cells are also discussed, with especial emphasis in the possible roles of organic acids in these processes. Both the possible causes and functions of the organic acid concentration increases in iron-deficient plants are reviewed.

Towards a knowledge-based correction of iron chlorosis

Iron (Fe) deficiency-induced chlorosis is a major nutritional disorder in crops growing in calcareous soils. Iron deficiency in fruit tree crops causes chlorosis, decreases in vegetative growth and marked fruit yield and quality losses. Therefore, Fe fertilizers, either applied to the soil or delivered to the foliage, are used every year to control Fe deficiency in these crops. On the other hand, a substantial body of knowledge is available on the fundamentals of Fe uptake, long and short distance Fe transport and subcellular Fe allocation in plants. Most of this basic knowledge, however, applies only to Fe deficiency, with studies involving Fe fertilization (i.e., with Fe-deficient plants resupplied with Fe) being still scarce. This paper reviews recent developments in Fe-fertilizer research and the state-of-the-art of the knowledge on Fe acquisition, transport and utilization in plants. Also, the effects of Fe-fertilization on the plant responses to Fe deficiency are reviewed. Agronomical Fe-fertilization practices should benefit from the basic knowledge on plant Fe homeostasis already available; this should be considered as a long-term goal that can optimize fertilizer inputs, reduce growers costs and minimize the environmental impact of fertilization.

Involvement of the ABCG37 transporter in secretion of scopoletin and derivatives by Arabidopsis roots in response to iron deficiency

Studies of Iron (Fe) uptake mechanisms by plant roots have focussed on Fe(III)-siderophores or Fe(II) transport systems. Iron deficency also enhances root secretion of flavins and phenolics. However, the nature of these compounds, their transport outside the roots and their role in Fe nutrition are largely unknown. We used HPLC/ESI-MS (TOF) and HPLC/ESI-MS/MS (ion trap) to characterize fluorescent phenolic-type compounds accumulated in roots or exported to the culture medium of Arabidopsis plants in response to Fe deficiency. Wild-type and mutant plants altered either in phenylpropanoid biosynthesis or in the ABCG37 (PDR9) ABC transporter were grown under standard or Fe-deficient nutrition conditions and compared. Fe deficiency upregulates the expression of genes encoding enzymes of the phenylpropanoid pathway and leads to the synthesis and secretion of phenolic compounds belonging to the coumarin family. The ABCG37 gene is also upregulated in response to Fe deficiency and coumarin export is impaired in pdr9 mutant plants. Therefore it can be concluded that: Fe deficiency induces the secretion of coumarin compounds by Arabidopsis roots; the ABCG37 ABC transporter is required for this secretion to take place; and these compounds improved plant Fe nutrition.

Iron chlorosis paradox in fruit trees

Abstract We have investigated the effect of iron (Fe) chlorosis on leaf Fe, leaf chlorophyll, leaf area, leaf thickness, leaf fresh and dry weight and specific leaf weight per area in young, fully developed leaves of Fe‐deficient and Fe‐sufficient peach (Prunus persica L. Batsch) and pear (Pyrus communis L.) trees growing in the field in northeastern Spain. Iron chlorosis decreased leaf chlorophyll concentration, fresh and dry weight per leaf and leaf area, whereas leaf thickness was practically unaffected. Chlorosis caused differences in leaf Fe concentrations that were best detected on a per leaf basis. Significant differences in Fe concentration could be detectable in pear on an area basis or a volume basis. However, when expressed on a per dry weight basis the Fe concentrations of control and chlorotic leaves were not significantly different. The fact that chlorotic leaves have less Fe per leaf confirms that the chlorotic trees are under a short supply of Fe. However, chlorotic fruit tree leaves have ...

Effects of Cd and Pb in sugar beet plants grown in nutrient solution: induced Fe deficiency and growth inhibition

Effects of Cd and Pb toxicity were investigated in sugar beet (Beta vulgaris L.) grown in hydroponics under growth-chamber-controlled conditions. Chemical speciation calculations were used to estimate the chemical species in equilibrium. Cd, used as chloride salt or chelated to EDTA, decreased fresh and dry mass of both root and shoot, and increased root / shoot ratios. Plants developed few brownish roots with short laterals. Cd decreased N, P, Mg, K, Mn, Cu and Zn uptake, and facilitated Ca uptake. Leaves of plants treated with 10 or 50 μM Cd-EDTA and 10 μM CdCl2 developed symptoms of Fe deficiency. These symptoms included decreased leaf chlorophyll (Chl) and carotenoid concentrations, increased carotenoid / Chl and Chl a/b ratios, de-epoxidation of violaxanthin cycle pigments, and decreased photosynthetic rates and PSII efficiency. Plants treated with 50 μM CdCl2, however, had decreased growth but did not show marked leaf Fe-deficiency symptoms. All Cd treatments increased Fe(III)-chelate reductase activity in root tips, although Fe concentrations in shoots were similar to those found in control plants. Pb chelated with EDTA induced visual symptoms only at concentrations of 2 mM. Leaves of Pb-treated plants remained green and their edges were rolled inwards. Pb increased root fresh and dry mass with no changes in shoot mass, therefore increasing the root / shoot ratio. Changes in plant nutrient concentrations with Pb were only minor, although leaf Cu levels approached critical deficiency levels. No symptoms of Fe deficiency were apparent in leaves. Root tips of Pb-treated plants, however, had increased Fe(III)-chelate reductase activities.

Agronomic means for the control of iron deficiency chlorosis in deciduous fruit trees

Abstract Iron deficiency induced chlorosis represents the main nutritional disorder in fruit tree orchards grown on calcareous and/or alkaline soils. Until rootstocks tolerant to Fe deficiency chlorosis are available for most susceptible fruit species, the agronomic means of preventing or curing Fe deficiency chlorosis will be considered of utmost importance by fruit growers. Chlorosis of fruit trees has been successfully controlled through foliar or soil applications of Fe chelates, which are expensive and have to be applied annually. In this paper results of research carried out within an EU joint research project are reported, where the effectiveness of alternative, low‐input, environmentally friendly management techniques to control Fe deficiency chlorosis has been tested in established kiwifruit, peach and pear orchards located in the Po Valley (Italy), in the Ebro Valley (Spain) and in the area of Imathia (Greece). Iron sulphate supply to the soil proved to be effective only if applied together with high amounts of organic matter such as compost or manure. Promising results in preventing chlorosis were obtained by sowing a mixture of graminaceous species along the tree row and supplying them with Fe sulphate. Laboratory tests indicated that long lasting decreases of pH in calcareous soils are difficult to achieve. We have also followed two approaches using foliar sprays: 1) testing a variety of compounds which may activate the Fe pool likely present in chlorotic leaves (citric, sulphuric, ascorbic and indole‐3‐acetic acid) and 2) applying Fe sources alternative to synthetic Fe chelates. Sprays aiming to activate the Fe pools in a chlorotic leaf were generally effective, although rarely caused a full recovery. This suggests that inactivation of Fe occurs outside the mesophyll cells. Sprays of Fe sulphate in all the crops tested showed similar or even higher regreening effect than FeDTPA.

Photosystem II efficiency in low chlorophyll, iron-deficient leaves

Iron deficiency (iron chlorosis) is the major nutritional stress affecting fruit tree crops in calcareous soils in the Mediterranean area. This work reviews the changes in PS II efficiency in iron-deficient leaves. The iron deficiency-induced leaf yellowing is due to decreases in the leaf concentrations of photosynthetic pigments, chlorophylls and carotenoids. However, carotenoids, and more specifically lutein and the xanthophylls of the V+A+Z (Violaxanthin+ Antheraxanthin+Zeaxanthin) cycle are less affected than chlorophylls. Therefore, iron-chlorotic leaves grown in either growth chambers or field conditions have increases in the molar ratios lutein/chlorophyll a and (V+A+Z)/chlorophyll a. These pigment changes are associated to changes in leaf absorptance and reflectance. In the chlorotic leaves the amount of light absorbed per unit chlorophyll increases. The low chlorophyll, iron-deficient leaves showed no sustained decreases in PS II efficiency, measured after dark adaptation, except when the deficiency was very severe. This occurred when plants were grown in growth chambers or in field conditions. However, iron-deficient leaves showed decreases in the actual PS II efficiency at steady-state photosynthesis, due to decreases in photochemical quenching and intrinsic PS II efficiency. Iron-chlorotic leaves were protected not only by the decrease in leaf absorptance, but also by down-regulation mechanisms enhancing non-photochemical quenching and thermal dissipation of the light absorbed by PS II within the antenna pigment bed.

Effects of zinc toxicity on sugar beet (Beta vulgaris L.) plants grown in hydroponics

The effects of high Zn concentration were investigated in sugar beet (Beta vulgaris L.) plants grown in a controlled environment in hydroponics. High concentrations of Zn sulphate in the nutrient solution (50, 100 and 300 microm) decreased root and shoot fresh and dry mass, and increased root/shoot ratios, when compared to control conditions (1.2 microm Zn). Plants grown with excess Zn had inward-rolled leaf edges and a damaged and brownish root system, with short lateral roots. High Zn decreased N, Mg, K and Mn concentrations in all plant parts, whereas P and Ca concentrations increased, but only in shoots. Leaves of plants treated with 50 and 100 microm Zn developed symptoms of Fe deficiency, including decreases in Fe, chlorophyll and carotenoid concentrations, increases in carotenoid/chlorophyll and chlorophyll a/b ratios and de-epoxidation of violaxanthin cycle pigments. Plants grown with 300 microm Zn had decreased photosystem II efficiency and further growth decreases but did not have leaf Fe deficiency symptoms. Leaf Zn concentrations of plants grown with excess Zn were high but fairly constant (230-260 microg.g(-1) dry weight), whereas total Zn uptake per plant decreased markedly with high Zn supply. These data indicate that sugar beet could be a good model to investigate Zn homeostasis mechanisms in plants, but is not an efficient species for Zn phytoremediation.

The pH Requirement for in Vivo Activity of the Iron-Deficiency-Induced "Turbo" Ferric Chelate Reductase (A Comparison of the Iron-Deficiency-Induced Iron Reductase Activities of Intact Plants and Isolated Plasma Membrane Fractions in Sugar Beet).

The characteristics of the Fe reduction mechanisms induced by Fe deficiency have been studied in intact plants of Beta vulgaris and in purified plasma membrane vesicles from the same plants. In Fe-deficient plants the in vivo Fe(III)-ethylenediaminetetraacetic complex [Fe(III)-EDTA] reductase activity increased over the control values 10 to 20 times when assayed at a pH of 6.0 or below (“turbo” reductase) but increased only 2 to 4 times when assayed at a pH of 6.5 or above. The Fe(III)-EDTA reductase activity of root plasma membrane preparations increased 2 and 3.5 times over the controls, irrespective of the assay pH. The Km for Fe(III)-EDTA of the in vivo ferric chelate reductase in Fe-deficient plants was approximately 510 and 240 [mu]M in the pH ranges 4.5 to 6.0 and 6.5 to 8.0, respectively. The Km for Fe(III)-EDTA of the ferric chelate reductase in intact control plants and in plasma membrane preparations isolated from Fe-deficient and control plants was approximately 200 to 240 [mu]M. Therefore, the turbo ferric chelate reductase activity of Fe-deficient plants at low pH appears to be different from the constitutive ferric chelate reductase.